In 1937, after two years of secret negotiations, the Marijuana Tax Act of 1937 became law.

We cannot understand yet, Mr. Chairman, why this bill should have been prepared in secret for 2 years without any intimation, even, to the profession, that it was being prepared.
Dr. William C. Woodward, representing the American Medical Association, to Representative Robert L. Doughton, Chairman, House Ways and Means Committee, during hearings on the Marijuana Tax Act of 1937.
http://www.druglibrary.org/schaffer/hemp/taxact/woodward.htm

For those who haven't already researched this topic, here's a short version of why this is an issue to begin with.

For a more complete version of the history of cannabis, read Jack Herer's fine book, The Emperor Wears No Clothes.  The on-line version is abbreviated.  Please buy a copy of the full text if you'd like to learn more.

Bear in mind, this only applies to the use of cannabis in the United States.  Cannabis has been used by man worldwide since the beginning of written history, about 5,000 years.  Evidence suggests that man's use of hemp extends another 2,000 years before we learned to write.

There seems to be a mystery as to why cannabis use ever came up as an issue in the first place. 

William Randolph Hearst used yellow journalism in his newspapers to throw racist rants against the Mexicans, but it was a small to non-existent issue in the public eye. Do you remember William Randolph Hearst?  I thought that name might ring a bell.  Remember, he's the newspaper baron of the late 19th and 20th centuries.  The man that Orson Welles modelled his character of Citizen Cane after.  The one who purportedly told the illustrator Frederic Remington, after asking to come home from Cuba because there wasn't a story, "You furnish the pictures and I'll furnish the war."  There were much bigger issues in 1937.  The Depression, Nazi Germany, et al. It can be equated to today's discussion of teens 'sexting', sending risqué pictures of themselves to friends using their cell phones.  Enough of an issue to cause parents concern, but not enough of an issue to raise a national cry to ban cell phones.

Like any mystery, first, follow the money.

To start with, the history of this country would be much different if it weren't for hemp.  Hemp possibly provided the power in the sailcloth and the riggings for Columbus's three ships, as it did for most ships of that era.  Hemp was a superior product to cotton for sea travel because it lasted far longer in the salt environment.  But hemp was expensive, relative to cotton, because it took much more labor to make the fiber useful from hemp than from cotton. 

From all know accounts, cannabis was here in the Americas long before Columbus.  In 1619, America's first hemp law was enacted.  No, marijuana wasn't prohibited.  Actually, it was against the law to refuse to grow cannabis. 

Cannabis was used to pay taxes in America for over 200 years.  In fact, you could be jailed for not growing cannabis during several periods of shortage.

Washington and Jefferson, Founding Fathers of America both, grew cannabis on their plantations.  It was their patriotic duty.  It was also the patriotic duty of American farmers to grow hemp during WWII as a source of rope and rigging for the Navy.  Watch the propaganda film "Hemp for Victory"

Throughout the 19th and early 20th centuries, cannabis was the number one, two or three medicine in the U.S.  Before the processing of morphine and the advent of the hypodermic needle during the Civil War, it was the number one medicine.  It remained the second most used medicine until the advent of aspirin in 1901, when it then moved to third.  Although the active compounds in cannabis remained unknown until 1967, it remained a very large part of this nation's health care system until 1937.  So now you know that the health benefits of cannabis are nothing new, at least to our ancestors.

For 72 years, since 1937, our culture has been taught by our Government that marijuana use causes insanity and death.  This propaganda ploy was started by Harry J. Anslinger, the first Commissioner of the Federal Bureau of Narcotics.  This comes after thousands of years of safe and beneficial human use of hemp, or cannabis sativa.

But you want to know why cannabis or marijuana is illegal in the US today.  Something really bad or sinister about cannabis must have been discovered.  Right?

The bad thing about cannabis was its usefulness and its threat to DuPont's nylon.

Have you ever heard of a guy named Harry Anslinger?  No, I thought not.

How about J. Edgar Hoover?  Anslinger was a contemporary of Hoover.  He wasn't accused of wearing dresses and heels like Hoover, but in his department he was just as influential.  Harry Anslinger was appointed first Director of the Federal Bureau of Narcotics (FBN), precursor to today's Drug Enforcement Agency (DEA).  He held this post for 32 years.

Harry had spent nine years working for various military and police organizations from 1917 to 1928.  He worked internationally, focusing on international drug trafficking.  In 1929, he went to work for the U.S. Bureau of Prohibition.  By this time, this bureau was racked with corruption and scandal.  Prohibition was becoming a failed experiment.  Harry's perceived integrity allowed him to rapidly advance.  In 1930, he was named to his FBN post, organized under the Department of the Treasury.  He became during his tenure a skilled tactician and bureaucrat.

Harry was a nephew-in-law of Andrew Mellon, Herbert Hoover's Secretary of the Treasury.  Andrew Mellon's name lives on today in the form of Mellon Bank, based in Pittsburgh, PA.  The Pittsburgh Penguins play in Mellon Arena.  Now you need to know that Mellon Bank is one of only two banks that DuPont has ever borrowed money from in its 190 year history.  Once was to buy control of General Motors in the 1920's. 

DuPont, in 1937, had just patented the process to make nylon.  Coincidentally, in the same year, machines to process hemp cheaply into fiber for the same purposes were becoming affordable and available.  This was an immediate threat to DuPont and their extended business plan.   Nylon is a fiber, similar to what can be processed from hemp.  Cheap hemp from a renewable source could have put a major dent into the potential market for a synthetic, fossil fuel derived alternative to cotton and silk that had, up to then, dominated the fiber market.  And it would have been a major disruption to DuPont's plans.  Also, DuPont had just patented new sulfate/sulfite processes for use in paper making from wood pulp.  Hemp makes great paper with much less chemicals needed.  All in all, these products wound up generating nearly 80% of DuPont's rail shipments for the next 60 years.

William Randolph Hearst had lost 800,000 acres of timber to Pancho Villa.  Villa had nationalized land Hearst owned in Mexico during his revolution for land for the peasant class.  While Hearst owned many newspapers, they didn't pay the dividends.  Mining, ranching and forestry accomplished that.  This enraged Hearst to the point of declaring a propaganda war against all Mexicans.  Hearst had spent ten years portraying Mexicans and negroes as lazy, cocaine loving people.  In 1930, he shifted to lazy, marijuana loving people.  Marijuana was, until then, a term relatively unknown in the U.S.  Americans knew it as cannabis or hemp.  Hearst cranked up the sensationalism to try to fuel public opinion against basically non-white people everywhere.

All this came to a head in 1937.  While there was still no public outcry for something to be done about the 'Marijuana problem', Anslinger had drafted and introduced a bill that would place a prohibitive tax on the production and sale of cannabis.   Preparation was done in secret and the bill, instead of being introduced in the House Finance Committee as tax bill or the Agricultural Committee as a farm bill was introduced inappropriately in the the House Ways and Means Committee for procedural reasons.  Meaning little debate and a quick vote.  In spite of the lack of publicity, the American Medical Association (AMA) still protested.  Their protests were quickly dismissed.  The Act passed with debate being limited to one question.  When asked if the AMA had been consulted, Representative Vinson, a strong DuPont proponent said, yes, they had and that they (the AMA) were in complete agreement.

This bill has led to subsequent laws that banned and criminalized the production, possession and use of this safest of medicines.  It has also removed a natural competitor of the coal, oil and paper industries.  It has led to immeasurable human suffering both directly through incarceration and seizure and indirectly through the loss of all the amazing properties of hemp to the human race.  Of these properties, the relaxation experienced by smoking cannabis may be the least important.